1. Field of the Invention
The present invention relates to a process for producing a charge control agent which comprises an azo-based iron complex salt having negative chargeability and high environmental safety.
2. Prior Art
In an image forming process of electrophotographic system employed in copiers and printers, the surface of a photoreceptor is charged (main charging), an electrostatic latent image corresponding to a target image is formed by exposure to light (image exposure), this electrostatic image is visualized by a charged toner (development), the formed toner image is transferred onto paper or plastic film (transfer), and the transferred toner image is fixed by heat or pressure (fixing) to obtain a target visible image.
In the above image forming process, an inorganic photoreceptor such as selenium, selenium alloy, cadmium sulfide or amorphous silicon, or an organic photoreceptor containing a charge generating agent and a charge transport agent is used as the photoreceptor.
Powders containing a colorant and another additive dispersed in a binder resin are used as a toner for development.
A typical example of the above additive contained in the toner is a charge control agent which is used to secure desired charging characteristics (such as charging risetime, charging level and charging stability).
Negatively chargeable azo-based metal complex salts (for example, azo-based complex salts such as iron, cobalt and chromium complex salts) are proposed as the charge control agent in Patent Documents 1 to 3.
When the above azo-based metal complex salts are used, the charging risetime of the toner can be accelerated, the toner can be fully negatively charged quickly, the amount of charge can be stabilized while it is suitably controlled, and a clear image can be formed while the development speed of an electrostatic latent image is accelerated. Out of these azo-based metal complex salts, an iron complex salt has high environmental safety and is of extremely great industrial value.
The charge control agent is also used in a powdery coating material which is used for electrostatic coating, charges in predetermined polarity, is coated on the surface of a target structure such as a car body by making use of electrostatic attractive force and can form a coating film on the surface of the structure by baking it. The excellent charging ability of the above-described negatively chargeable azo-based charge control agent is exhibited even for this powdery coating material.